1. Field of the Invention
Embodiments of the present invention generally relate to methods and apparatus of connecting wellbore tubulars by explosive welding. More specifically, the present invention relates to apparatus and methods for joining together the ends of wellbore tubulars by explosive welding and reforming a connection between the tubulars. More particularly still, the present invention relates to methods and apparatus of joining together the ends of wellbore tubulars by explosive welding while using a frangible anvil.
2. Description of the Related Art
In order to access hydrocarbons in subsurface formations, it is typically necessary to drill a borehole into the earth to some predetermined depth adjacent a hydrocarbon-bearing formation. The process of drilling a borehole and of subsequently completing the borehole in order to form a wellbore requires the use of various tubular strings. While the depth of a typical borehole reaches several thousand feet, the length of an individual tubular is only approximately thirty feet. Therefore, in the construction, completion, and production phases of oil or gas wells it is usually necessary to assemble long strings of tubulars that include drill pipe, casing, production tubing, and liner. Due to the length of these tubulars, sections or stands of tubulars are progressively added to the tubular string as it is lowered into the well from a drilling platform.
When it is desired to add a section or stand of tubular, a string of tubulars is usually restrained from falling into the well by applying the slips of a spider located in the floor of the drilling platform. The new section or stand of tubular is then moved from a rack to the well center above the spider and placed on top of the string using a top drive adapter. Next, the new tubular is connected to the tubular string and the entire tubular string lowered into the well by using an elevator to lift the tubular string slightly to enable the slips of the spider to be released prior to lowering the tubular string. Once the top of the new tubular is adjacent the spider, the slips of the spider are re-applied, the elevator is disconnected, and the process repeated until the joined tubulars form a tubular or casing string of desired length.
Each tubular is filled with fluid as it is run into the wellbore to maintain pressure in the wellbore and prevent collapsing due to high pressures within the wellbore. In order to circulate the drilling fluid, the top of the tubular string must be sealed so that the tubular string may be pressurized with drilling fluid. Since the tubulars are under pressure, the integrity of the seal is critical to safe operation and to minimize the loss of expensive drilling fluid. Once the tubulars are in position downhole, the mechanical and seal integrity of the jointed connections are critically important since any failures in connections become difficult and costly to fix.
As the tubulars are joined and lowered into the hole, the tubulars may become stuck. When this occurs, load or weight must be added to the tubular string to force the tubulars into the wellbore or drilling fluid must be circulated down the inside diameter of the tubular and out of the tubular into an annulus in order to free the tubular from the wellbore. Therefore, special rigging has traditionally been installed to axially load the tubular string or to circulate drilling fluid.
Typically threaded connections are used to connect multiple tubular members end-to-end. This is usually accomplished by providing tubulars that have a simple male to female threaded connection. These tubulars are connected, or “made-up,” by transmitting torque against one of the tubulars while the other tubular is held stationary. Torque is transmitted in a single direction in accordance with the direction corresponding with connection make-up. Any torque applied to the joint in the make-up direction will have the effect of continuing to tighten the threaded joint. Tubular joints are susceptible to leaking and mechanical failures due to, among other things, over-torquing. Commonly used thread connections with internally and externally flush screw thread connections form weak spots with a significantly lower strength than the rest of the tubular. Further, connecting screw thread casing at the drilling floor consumes time and requires carefully machined tubulars.
Since there are problems associated with jointed tubulars, explosive welding techniques present an alternative for forming a connection between the tubulars. Explosive welding of pipes requires either locating an explosive charge internally in conjunction with an external supporting “anvil” and leading detonating wires out of the end of the tubular or utilizing an external explosive charge in conjunction with an internal anvil that is either subsequently withdrawn from the tubular or left in the inside diameter of the tubular. However, these approaches present feasibility problems with wellbore tubular make-up on a rig floor where machinery, space, and time are at a premium. Leading the detonating wires out of tubulars or removing the anvil from the inside diameter of the tubular requires both time and equipment. In addition, leaving an internal anvil within the inside diameter of a wellbore tubular creates a restriction that can impede fluid flow and can effect subsequent tool passage through the tubular. Therefore, it would be useful to be able to explosively weld wellbore tubulars together using a disposable interior anvil or integrate a removable anvil with other individual devices needed at the wellbore.
One drawback of the bonding or welding process for joining tubulars is that an inside diameter and an outside diameter of the tubular connection can become distorted. This distortion occurs due to the intense pressure or heat applied to the tubulars when joining them. Distortion of the inner diameter of the tubulars is problematic because it may minimize the production capacity of the well and cause tools and smaller tubulars to snag when lowered through the tubular. Similarly, distortion of the outer diameter may cause the tubular to snag when lowered through the wellbore.
Therefore, there exists a need for apparatus and methods to facilitate the joining of tubulars by explosive welding. There exists a further need for apparatus and methods for explosive welding of wellbore tubulars that uses an anvil that does not require retrieval. Further still, there exists a need for apparatus and methods for correcting the distortions created by the joining of tubulars by explosive welding.